1. Field of the Invention
The present invention relates to structures of a die pickup apparatus for picking up semiconductor dies and methods for picking up semiconductor dies.
2. Description of Related Art
Semiconductor dies are typically manufactured by dicing a wafer of 6 or 8 inches into dies of a predetermined size. When dicing a wafer, an adhesive dicing tape is attached on a back surface of the wafer so as to prevent the manufactured semiconductor dies from falling apart, and then the wafer is cut from the other side using such as a dicing saw. At this time, the dicing tape attached to the back surface of the wafer is slightly cut into its surface but not entirely cut off, and the semiconductor dies remain held on the tape. Then, the individual semiconductor dies are picked up one by one from the dicing tape and transferred to a subsequent step such as a die bonding step.
Conventionally, a method using a push-up needle is widely employed as a method of picking up semiconductor dies from an adhesive dicing tape (see FIG. 15 of Japanese Patent No. 3209736, for example). According to this method, semiconductor dies are picked up using a collet in such a manner that a semiconductor die is pushed upward in its center by a push-up needle under a dicing sheet to which a tensile force is exerted toward its periphery while the semiconductor die is suctioned by a collet, and thus the semiconductor die is separated from the adhesive dicing sheet by the tensile force exerted to the dicing sheet.
However, this method of using the push-up needle has become less suitable for picking up low-profile semiconductor dies of recent years, because the method poses a problem that the pushing up can break the semiconductor dies when the dies are made thin.
To address this issue, methods have been proposed with which semiconductor dies are removed and picked up from an adhesive dicing sheet without using a push-up needle. For example, Japanese Patent No. 3209736 proposes a method including: placing a semiconductor die to be picked up over a plurality of suction holes provided for a stage; producing vacuum in the plurality of suction holes to deform a dicing sheet by suctioning the sheet into the suction holes while the semiconductor die is suction-held by a collet; separating the dicing sheet corresponding to the suction holes from the semiconductor die; and then separating the remaining portion of the dicing sheet from the semiconductor die by moving the stage horizontally or rotationally (see FIG. 1 through FIG. 4 of Japanese Patent No. 3209736).
Japanese Patent No. 3209736 also proposes a different method including: providing a projection on a surface of the stage, the projection having a width narrower than that of a semiconductor die to be picked up; providing suction holes that surround the projection on the surface of the stage; when picking up a semiconductor die, placing a semiconductor die to be picked up over the projection so as to cover an area larger than the projection and suction-holding the semiconductor die to be picked by a collet; suctioning the dicing sheet downward by vacuum through the suction holes and separating a portion of the dicing sheet that protrudes outside an area corresponding to the projection from the semiconductor die; and then moving the projection in parallel with the surface of the stage while suctioning the semiconductor die to be picked by the collet, thereby separating the remaining portion of the dicing sheet from the semiconductor die (see FIG. 9 and FIG. 10 of Japanese Patent No. 3209736).
The method disclosed in Japanese Patent No. 3209736 is to separate the dicing tape from the semiconductor die by producing vacuum in the suction holes to suction the dicing tape into the suction holes. However, once separated from the semiconductor die, the dicing tape covers opening of the suction holes, and consequently it is not possible to suction air around the suction holes after separating portions of the dicing tape immediately above the suction holes. Therefore, while the portions of the dicing sheet immediately above the suction holes can be separated by the suctioning, a portion of the dicing sheet covering around the suction holes cannot be separated by the vacuum suction through the suction holes and remains adhered to the semiconductor die (see FIG. 1 and FIG. 2 of Japanese Patent No. 3209736). In contrast, in the case in which the remaining portion of the dicing sheet is separated by moving the stage, it is possible to reduce the damage caused to the semiconductor die if an area of the remaining portion is smaller, as force exerted to the semiconductor die can be made smaller. However, in order to make the remaining portion after separating the dicing sheet through the suction holes smaller, it is required to provide a suction hole of a size corresponding to a size of the semiconductor die to be picked up. Suctioning the dicing sheet through such a large suction hole may, when adhesive force of the dicing sheet is large, produce a large force that is exerted to the semiconductor die. Semiconductor dies of recent years are particularly made thinner with less intensity, and such a large force may break or deform the semiconductor dies. As described above, with the method disclosed in Japanese Patent No. 3209736, a large force is exerted to the semiconductor die either during the suctioning when a large suction hole is used or during the movement of the stage when small suction holes are used, and therefore the force exerted to the semiconductor die during the separation of the dicing sheet cannot be controlled. This poses a problem that the semiconductor die can be adversely damaged.
Moreover, according to the other method disclosed in Japanese Patent No. 3209736, the portion of the dicing sheet of the semiconductor die that protrudes outside the area corresponding to the projection is separated by producing vacuum in the small suction holes provided only around the projection, and the remaining portion of the dicing sheet of the semiconductor die is separated by the tensile force exerted to the dicing sheet. Accordingly, it is necessary to increase the height of the projection in order to separate the dicing sheet without fail. However, when an adjacent semiconductor die is present in a direction toward which the projection moves, the projection can be brought into contact with the adjacent semiconductor die and damages the semiconductor die. Therefore, the height of the projection is limited, and it is adversely not possible to separate the dicing sheet without fail.